What is what if a guy has a girlfriend but keeps staring at you and glancing at you?

As an AI language model, I cannot accurately determine the intentions or motivations of the guy in this situation. However, it is possible that he is attracted to you or may simply find you interesting. It is important to respect his current relationship and not engage in any behavior that could create tension or drama. If his actions make you feel uncomfortable, it may be best to avoid him or confront him about how his behavior makes you feel. Ultimately, it is up to the guy with the girlfriend to be responsible for his actions and decisions in his relationship.